As a way to combat global warming, introduction of new energy such as solar photovoltaic power generation and wind power generation has been promoted in recent years throughout the world. Since outputs of these power generations are affected by the weather, it is predicted that introduction on a large scale will cause problems with operation of power systems such as difficulty in maintaining frequencies and voltages. As a way to address such problems, installation of large-capacity storage batteries for smoothing output variations, storing surplus power, and load leveling is expected.
An RE battery is one of large-capacity storage batteries. FIG. 6 shows the form of a conventional RF battery disclosed in Patent Document 1 (Japanese Patent Laying-Open No. 2001-43884). As shown in FIG. 6, a conventional RF battery 100 includes a battery element 100c with a membrane 101 interposed between a positive electrode cell 102 having a positive electrode 104 therein and a negative electrode cell 103 having a negative electrode 105 therein, and a circulation mechanism (tanks 106, 107; upstream pipes 108, 109; downstream pipes 110, 111; pumps 112, 113). RF battery 100 can be charged and discharged by means of the circulation mechanism to supply a positive electrode electrolyte and a negative electrode electrolyte to battery element 100c by circulation. An aqueous solution containing a metal ion such as a vanadium ion having a valence which changes by oxidation-reduction is typically used as the electrolytes. The ions in tanks 106 and 107 in FIG. 6 are for illustrative purposes only. In FIG. 6, solid line arrows indicate charge, and broken line arrows indicate discharge.
In conventional RF battery 100, upstream pipes 108 and 109 for supplying the positive and negative electrode electrolytes to battery element 100c have one ends attached to the bottom sides (lower sides) of tanks 106 and 107, respectively, and the other ends attached to the bottom side (lower side) of battery element 100c. Furthermore, in conventional RF battery 100, downstream pipes 110 and 111 for returning the electrolytes from battery element 100c to tanks 106 and 107 of both electrodes are attached to the upper sides of tanks 106 and 107, respectively.